Treatment of subterranean formations

Abstract

A method of treating a subterranean formation by contacting the formation with the following: (a) ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) sulfamic acid.

Claims

1. A method of treating a subterranean formation, the method comprising: (a) introducing an ammonium compound into the formation; (b) introducing an oxidizing agent into the formation, wherein said oxidizing agent is selected from a perchlorate and a nitrite or combinations thereof; (c) introducing sulfamic acid as a solution or slurry in water into the formation; and (d) contacting the formation with said ammonium compound, said oxidizing agent and said sulfamic acid; wherein said ammonium compound reacts with said oxidizing agent and/or said sulfamic acid to generate a gas in the formation; wherein said sulfamic acid reacts to produce a gas, wherein the gas produced includes nitrogen atoms originating in the sulfamic acid; and wherein a ratio (B) defined as the number of moles of ammonium compound divided by the total number of moles of sulfamic acid contacted with the formation is greater than 0 and is 10 or less.

2. The method according to claim 1, wherein the method comprises treating the formation to create or enhance a fracture in the formation.

3. The method according to claim 2, wherein in the method the sum of the wt % of a formulation (F1) comprising said ammonium compound, a formulation (F2) comprising said oxidizing agent and a formulation (F3) comprising said sulfamic acid introduced into the formation is at least 98 wt %, of the total weight of materials introduced into the formation.

4. The method according to claim 1, wherein said oxidizing agent comprises a nitrite which, optionally, is sodium nitrite.

5. The method according to claim 1, wherein said ammonium compound and said oxidizing agent are contacted so they react and nitrogen and carbon dioxide are generated in the formation.

6. The method according to claim 1, wherein a ratio (A) defined as the number of moles of ammonium compound divided by the number of moles of nitrite contacted with the formation and/or reacted in the formation is in the range 0.05 to 2.0.

7. The method according to claim 1, wherein said ammonium compound is selected from ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, ammonium nitrate, ammonium sulfate, ammonium hydrogen sulfate, ammonium carbonate, ammonium carbamate, ammonium bicarbonate, ammonium hydroxide, ammonium acetate, ammonium borates, ammonium chromate, ammonium dichromate, ammonium cyanides, ammonium glutamate, ammonium molybdate, ammonium oxalate, ammonium hydrogen oxalate, ammonium phosphate monobasic, ammonium phosphate dibasic, ammonium thiosulfate, ammonium formate, ammonium sulfamate, ammonium sulfite, ammonium persulfate, ammonium sulfide, ammonium tartrate dibasic, ammonium thiocyanate, ammonium dihydrogen phosphate and ammonium glycinate or mixtures thereof.

8. The method according to claim 1, wherein said ammonium compound includes, in addition to a NH.sub.4.sup.+ moiety, a second moiety which is arranged to generate a gas on reaction with said oxidizing agent and/or said sulfamic acid.

9. The method according to claim 8, wherein said second moiety comprises a sulfamate, carbonate or bicarbonate moiety.

10. The method according to claim 1, wherein a ratio (C) defined as the number of moles of ammonium compound divided by the sum of the number of moles of sulfamic acid which react with other materials contacted with the formation to produce a gas is greater than 0 and is 10 or less.

11. The method according to claim 1, wherein said ammonium compound is provided as a slurry, an emulsion or a solution; and wherein the method comprises selecting an aqueous solution of said oxidizing agent.

12. The method according to claim 1, wherein: the sum of the total weight in grams (g) of ammonium compound, oxidizing agent and sulfamic acid introduced into the formation is herein referred to as SUM-W; the sum of the total volume in cm.sup.3 of gas generated by reaction of ammonium compound, oxidizing agent and said sulfamic acid is herein referred to as SUM-V; wherein, in the method, the Reaction Efficiency is defined as SUM-V divided by SUM-W; wherein the Reaction Efficiency is at least 100 cm.sup.3/g and is less than 300 cm.sup.3/g.

13. The method according to claim 1, wherein said ammonium compound is ammonium bicarbonate and the method comprises producing pulses of pressure within the formation by controlling contact and/or amounts of ammonium bicarbonate, oxidizing agent and/or sulfamic acid within the formation.

14. The method according to claim 1, wherein said ratio (B) is less than 2.0.

15. A method of treating a subterranean formation, the method comprising: (a) introducing an ammonium compound into the formation; (b) introducing an oxidizing agent into the formation, wherein said oxidizing agent is selected from a perchlorate and a nitrite or combinations thereof; (c) introducing sulfamic acid as a solution or slurry in water into the formation; and (d) contacting the formation with said ammonium compound, said oxidizing agent and said sulfamic acid; wherein said ammonium compound reacts with said oxidizing agent and/or said sulfamic acid to generate a gas in the formation; wherein said sulfamic acid reacts to produce a gas, wherein the gas produced includes nitrogen atoms originating in the sulfamic acid; and wherein a ratio (H) defined as the number of moles of oxidizing agent divided by the total number of moles of sulfamic acid contacted with the formation is in the range 0.5-10.

16. The method according to claim 15, wherein said ratio (H) is in the range 0.75 to 3.5.

17. The method according to claim 15, wherein said oxidizing agent comprises a nitrite which, optionally, is sodium nitrite.

18. A method of treating a subterranean formation, the method comprising: (a) introducing an ammonium compound into the formation; (b) introducing an oxidizing agent into the formation, wherein said oxidizing agent is selected from a perchlorate and a nitrite or combinations thereof; (c) introducing sulfamic acid as a solution or slurry in water into the formation; and (d) contacting the formation with said ammonium compound, said oxidizing agent and said sulfamic acid; wherein said ammonium compound reacts with said oxidizing agent and/or said sulfamic acid to generate a gas in the formation; wherein said sulfamic acid reacts to produce a gas, wherein the gas produced includes nitrogen atoms originating in the sulfamic acid; wherein a ratio (B) defined as the number of moles of ammonium compound divided by the total number of moles of sulfamic acid contacted with the formation is greater than 0 and is 10 or less; and wherein a ratio (H) defined as the number of moles of oxidizing agent divided by the total number of moles of sulfamic acid contacted with the formation is in the range 0.5-10.

19. The method according to claim 18, wherein said ratio (B) is less than 2.0 and said ratio (H) is in the range 0.75 to 3.5.

20. The method according to claim 19, wherein said oxidizing agent comprises a nitrite.

21. The method of treating a subterranean formation according to claim 19, to generate gas within the formation so as to create or enhance a fracture in the formation, undertake a Huff and Puff operation or reduce proppant settling, wherein said ammonium compound includes, in addition to a NH.sub.4.sup.+ moiety, a second moiety which generates carbon dioxide or nitrogen on reaction with said oxidizing agent and/or said sulfamic acid; wherein: the sum of the total weight in grams (g) of ammonium compound, oxidizing agent and sulfamic acid introduced into the formation is herein referred to as SUM-W; the sum of the total volume in cm.sup.3 of gas generated by reaction of ammonium compound, oxidizing agent and said sulfamic acid is herein referred to as SUM-V; wherein, in the method, the Reaction Efficiency is defined as SUM-V divided by SUM-W; wherein the Reaction Efficiency is at least 100 cm.sup.3/g and is less than 300 cm.sup.3/g.

22. The method according to claim 18, wherein said oxidizing agent comprises a nitrite which, optionally, is sodium nitrite.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Specific embodiments of the invention will now be described, by way of example, with reference to:

(2) The FIGURE includes a graph showing gas volume generated for Examples 4 to 8.

WORKING EXAMPLES

(3) A subterranean formation may be treated with reagents which are arranged to react to produce a gas and/or heat within the formation. This may stimulate the formation by improving a fracture network within the formation, for example by creating new fractures, extending existing fractures, opening up naturally-occurring fractures or creating microfractures. The examples which follow describe reagents which may be used in a treatment.

Example 1General Procedure for Undertaking Reactions

(4) 10 mmol of an ammonium compound and 30 mmol of a nitrite or perchlorate-containing compound were added to a round-bottom flask and dissolved in the minimum quantity of water. Suitable apparatus to measure gas released was arranged in position and the solution heated with stirring to 75? C. Once the solution had reached 75? C., 20 mmol of an acid was also heated to 75? C. and injected into the reaction vessel. The quantity of gas generated was recorded.

Examples 2 and 3Comparison Between Using Hcl and Sulfamic Acid

(5) In order to compare use of sulfamic acid and HCl, sulfamic acid was reacted with ammonium chloride, ammonium bicarbonate and ammonium sulfamate in example 3 and the gas volume determined. For comparison purposes, in Examples 2, the same reaction and assessment was undertaken wherein the sulfamic acid was replaced with HCl.

(6) TABLE-US-00001 Gas generated Gas generated Gas generated when reacted when reacted when reacted with Ammonium with Ammonium with Ammonium Example Chloride/cm3 Bicarbonate/cm3 Sulfamate/cm3 2-HCl 330 560 920 (comparative) 3-Sulfamic acid 960 1360 1320

(7) It will be appreciated from Examples 2 and 3 that use of sulfamic acid results in increased levels of gas generation compared to reactions wherein sulfamic acid is replaced with commonly used hydrochloric acid.

Examples 4 to 8

(8) The reaction investigated was the reaction between ammonium bicarbonate, sodium nitrite and sulfamic acid. The effect of changing the quantities of sulfamic acid was investigated, using the general procedure described in Example 1.

(9) A summary of reagents used is provided in the table below:

(10) TABLE-US-00002 Ammonium bicarbonate Sodium nitrite Sulfamic acid Example No. mmol mmol mmol 4 10 10 5 5 10 10 7.5 6 10 10 10 7 10 10 20 8 10 10 25

(11) Results are provided in the FIGURE, from which it is noted that there is no significant improvement in gas generation beyond 20 mmol sulfamic acid, implying a preferred ammonium bicarbonate to sulfamic acid ratio of 1:2.

Examples 9 and 10Comparison Between Using Hcl and Sulfamic Acid at 1:2:4 Ratio of AMMONIUM SULFAMATE:ACID:SODIUM NITRITE

(12) A comparison of the performance of sulfamic acid and HCl were undertaken at the preferred ratios (as determined in other experiments not detailed) of 1:2:4 ratio of ammonium sulfamate:acid:sodium nitrite.

Example 9

(13) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution was heated to 75? C. Once the solution had reached 75? C., 0.83 mL of a 12 M aqueous solution of hydrochloric acid (10 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded. The reaction efficiency was calculated by dividing the gas quantity by mass of reagents used.

Example 10

(14) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution was heated to 75? C. Once the solution had reached 75? C., 4.75 mL of a 2.11 M aqueous solution of sulfamic acid (10 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded. The reaction efficiency was calculated by dividing the gas quantity by mass of reagents used.

(15) The table below details the results.

(16) TABLE-US-00003 Gas Efficiency/ mmol mmol mmol generated/ Total cm.sup.3 per Example NH.sub.4NH.sub.2SO.sub.3 NaNO.sub.2 Acid acid cm.sup.3 mass/g g 4 (comparative) 5 20 Hydrochloric 10.0 460 2.95 156 5 5 20 Sulfamic 10.0 750 2.92 257

(17) The results show that sulfamic acid is significantly advantageous over use of hydrochloric acid, in terms of volume of gas generated and reaction efficiency.

(18) The reagents described herein may be used in treatment of a formation as described. Reagents may be delivered in receptacles to a well-head for subsequent injection, for example using coiled tubing as described herein, into the formation. Exemplary compositions including concentrations and amounts in pound (lb) are detailed in the table below. Pounds (lb) can be converted to kg by multiplication by 0.45.

(19) TABLE-US-00004 Mass of Amount of Acid acid 0.83M Amount of conc/ solution/ NH.sub.4HCO.sub.3 2.50M NaNO.sub.2 Composition Acid M lb solution/lb solution/lb Eg 11 Sulfamic 2.11 8130 2531 6626

(20) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.